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PHOENIX (AP) -- A psychologist who diagnosed Jodi Arias with post-traumatic stress disorder and amnesia defended his work Monday as the prosecutor continued to question his credibility, repeatedly pointing out how the witness made errors on a test used to come to his conclusion.

Arias faces a possible death sentence if convicted of first-degree murder in the June 2008 killing of Travis Alexander in his suburban Phoenix home. Authorities say she planned the attack on her lover in a jealous rage. Arias initially told authorities she had nothing to do with it then blamed it on masked intruders. Two years after her arrest, she said it was self-defense.

Psychologist Richard Samuels, a defense witness, answered more than 100 juror questions last week. Most of the questions focused on Arias' lies and how Samuels could be sure she was telling the truth during his evaluation of the defendant, and whether she is telling the truth now.

Arizona is one of a few states where jurors have the legal right to query witnesses through written questions read by the judge.

Prosecutor Juan Martinez has spent several days picking apart Samuel's evaluation techniques, and even accusing the witness of forming a relationship with Arias that biased his diagnosis.

Samuels has denied the allegations, and testified that he based his diagnosis of Arias on multiple interviews with her, reviews of crime scene photos and police reports, as well as the tests he performed on her.

However, Martinez noted how Samuels had different scores for the same test he calculated at least three times.

"You got it wrong ... didn't you?" Martinez asked Monday.

"Yeah," Samuels replied.

"You were a little bit sloppy right?" Martinez prodded.

"I made an arithmetic error which does not affect the utility of the test," Samuels insisted, adding that regardless of the changing scores due to his calculation errors, Arias still would have been diagnosed with PTSD. "Each time that I scored it, Ms. Arias met or even exceeded the minimum criteria for the diagnosis of post-traumatic stress disorder."

Samuels testified previously that his diagnosis of PTSD and amnesia explains why Arias can't recall many details from the day she killed Alexander as the defense works to convince jurors the defendant may have lied repeatedly before, but she isn't lying now.

Jurors asked several questions last week related to whether Arias could suffer from the same ailments if she planned the killing, as the prosecution contends, or if it was indeed self-defense.

Samuels said it was possible, but unlikely.

Alexander suffered nearly 30 knife wounds, was shot in the head and had his throat slit. Arias' palm print was found in blood at the scene, along with her hair and nude photos of her and the victim from the day of the killing.

Arias said she recalls Alexander attacking her in a fury after a day of sex. She said she ran into his closet to retrieve a gun he kept on a shelf and fired in self-defense but has no memory of stabbing him.

She acknowledged trying to clean the scene, dumping the gun in the desert and working on an alibi to avoid suspicion. She said she was too scared and ashamed to tell the truth at the time but insists she isn't lying now.

However, none of Arias' allegations of Alexander's previous physical abuse, that he owned a gun and had sexual desires for boys has been corroborated during the trial that began in early January.